Alloys for metal to glass seals



Patented Apr. 29, 1941 stares PATENT QFFlCE ALLOYS FOR METAL 1'0 GLASS SEALS Victor Allen, Madison, and Charles P. Marsden,

.ln, Bloomfield, N. 3., assignors to Wilbur B.' a Driver 00., Newark, N. J, a corporation of New Jersey I No Drawing. Application September 6, 1940, Serial No. 355,668

7 Claims.

This invention relates to metallurgy and more particularly to the metallurgy of fir-containing alloys of the iron group metals and to a method of degasifying the same without deleteriously affecting the adherence and the chemical and physical properties of the surface oxide film on said alloys thereby to better condition the same for use in the forming of metal to glass seals.

One of the objects of the present invention is to provide an improved method for degasifying said alloys. Another object is to provide a degasified alloy product having a surface oxide film that is firmly adherent to the metal surface and capable of forming a gas impervious seal with glass. Still another object is to provide a Cr-containing alloy of the iron group metals adapted for use in the forming of metal to glass seals. Another object is to provide an improved metal to glass seal- Other objects and advantages will be ap of the wire must be provided with anadherent film of oxide to securely bind the glass and metal surfaces together and moreover the oxide film and the metal must be substantially free of gas and of compounds reactive with the glass to form gaseous products at the temperatures employed in the forming of the seal.

Heretofore in the art various chromium-containing alloys of the iron group metals have been proposed for use in the forming of metal to glass seals of the various types utilized in the lamp, radio tube, and gaseous conduction and electron discharge device industry, for the reason that chromium alloys are generally characterized by an adherent film of oxide. .One of the most satisfactor'y of such alloys from acoefiicient of ex- ,pansion viewpoint for use with lead glass of the type known in the art by the code numbers G l and G -12, in the forming metal to glass seals teristics of the surface oxide film on the alloy and the adherence'of the film to the metal surface.

We have discovered that degasification of the alloy while in the molten state by the use of metallic degasification agents requires generally the use of a sumcient excess of the agent to provide at least fractional alloyed percentages of the agent in the solidified metal to take care of dissolved gases liberated on solidification. The

surface oxide film formed subsequently on the solidified degasified alloy prior to the forming of the metal to glass seal is comprised at least in part of the oxide compounds of the alloyed percentages of degasifier agents remaining in the alloy and we have found that the presence of these oxide compounds of the degasifier agent materially alters the adherence and the chemical and physical properties of the normal Cr.Ni.Fe oxide film present on the surface of the alloy and the sealing properties of the film to glass.

We have discovered that by. using metallic beryllium as a degasifier agent for such alloys or by using aluminum and beryllium together as degasifier agents, residual alloyed percentages of the same as high as about 1% may be employed without detrimental effect to the sealing prop erties of the surface oxide-film or to the adherence of this film tovthe metal surface and with certain pos'itive benefits thereto. We have further found that the fractional percentages up to about 1% of alloyed beryllium are beneficial as a precipitation hardening agent in the alloy, permitting the use of smaller diameter wires or thinner sheet material than has heretofore been permissible with such type alloys.

' In accordance with the above discoveries, to produce the improved alloy product of the present invention the chromium-containing alloy of the iron group metals, as for example the ironchromium-nickel alloy above noted as being comprised of Cr 5-6%, Ni 42-43%, balance Fe, is produced in the customary manner by first forming a, molten substantially pure iron bath and adding the required percentages of nickel and chromium thereto. Considerable care must be taken to eliminate from the bath substantially all associated metal and metalloid impurities. In commercial practice, however, fractional percentages of the elements carbon, sulfur, phosphorus, manganese, boron, titanium and silicon will usually be pre'sent in the alloy, each in amounts not exceeding about 20%.

To the molten Cr.Ni;Fe alloy thus formed, beryllium is added in an amount at least suffiskimmed off from the molten metal and the degasified and scorified metal is cast into ingots. The cast metal then is worked down to desired wire sizes as heretofore practiced in the art, with the exception that prior to any cold mechanical deformation the metal must be annealed at temperatures approximating 7Q0-900 C. for a time intervalrequired to effect solution of the beryllium content and then rapidly cooled to atmospheric temperatures to retain the beryllium in solid solution. Extensive cold mechanical deformation may then be effected without difficulty.

As a modification of this practice, we have found that the molten alloy may be degasified with aluminum prior to the addition of the beryllium thereto, thereby effecting a material sav ing in the amount of the beryllium employed.

Other degasifying agents such as Mn, Si, Ti, Zr, B and the like are not to be considered substantial equivalents for Al in the present invention as they have been found to be detrimental to the adherence and glass scaling properties of the normal oxide film of these alloys when used either alone ,or in combination with beryllium.

As a specific embodiment of the practice of th present invention, we have found that in the Cr.Ni.Fe alloy containing -6% Cr, 42-43% Ni, balance substantially all iron except for fractional percentages up to about 1% of unavoidable metal and metalloid impurities, beryllium in fractional percentages up to about 1% may be incorporated without detriment to the glass sealing or film adherence properties of the normal oxide film of the alloy. As the beryllium content increases, the precipitation hardening advantage of this constituent increases and we have found that between .50-.75% is the most satisfactory range of beryllium for this result.

We have found it desirable to lower the chromium content of the alloy with increase in the beryllium content in order to maintain the ther-' mal coefiicient of expansion of the 'alloy substantially constant. For example, with Be as high as 1% the Cr content is preferably lowered to about 5% and with Be as low as 25% the Cr content may be as high as 5.75% but is within the range 5.255.50%.

Where the alloy has been degasified with aluminum prior to the addition of beryllium thereto, the aluminum content of the degasified and solidified alloy should not exceed about .25%, and preferably is within the range .10 to .20%. With this aluminum content, we have found that as low as .30% Be will produce substantially equivalent precipitation hardening results as .50% Be in the absence of aluminum.

Our preferred alloy composition for use in the forming of metal to glass seals comprises Cr 5.0- 5.25%, Ni 42%, Be .50%, balance substantially pure Fe. Another preferred alloy composition comprises Cr iii-5.25%, Ni 42%, Al '.20%, Be 30%, balance substantially pure Fe. Ineach of these alloys the total carbon, sulfur, phosphorus, manganese and silicon should be present in substantially residual amounts.

In'the forming of a metal to glass seal utilizing preferably this alloy and lime glass, the surface of the alloy is thoroughly cleaned, a relatively thin oxide film is formed thereon, preferably byv heating under oxidizing conditions to elevated temperatures, and glass is fused and pressure molded onto the oxidized metal surface, as heretofore practiced in the art. The Be and Al oxides present in the oxide film will be found to be nondeleterious to the adherence of the film to the metal surface and to the sealing properties of the film with the glass. The presence of the Be in the metal inhibits the evolution of gas from the metal at the sealing temperatures employed and it will be found that the sealing temperature employed is sufficientto induce precipitation hardening of the metal by the formation of Ni and Cr beryllide compounds. To condition the alloy for the maximum beneficial effects incident to this precipitation hardening, the alloy prior to scaling into glass should be subjected toa Be-solutioning heat treatment at temperatures within the range 700-900 C. followed by quick cooling. Such heat treatment may be 'done under oxidizing conditions, if desired, to simultaneously produce on the surface of the metal the desired thickness and character of oxide film best adapted for sealing.

to glass.

Having hereinabovedescribed the present invention generically and specifically, it is believed apparent that many modifications and departures may be made therein without departing essentially from the nature and scope thereof and all such are contemplated as may fall within the scope of the following claims.

What we claim is:

1. The method of forming a substantially gasfree alloy comprised of Cr 56%, Ni 42-43%, balance substantially all iron which comprises forming a molten bath comprised of the said constituents in the desired percentages and adding aluminum and beryllium thereto each in an amount at least sufficient to provide a relatively small alloyed percentage up to about 25% of Al and a relatively larger alloyed percentage up to about 1% of Be in the solidified alloy, treating the molten alloy with a flux to remove therefrom the Al and Be compounds formed, and then casting and solidifying the alloy.

2. As an article of manufacture, an alloy suitable foruse inthe forming of metal to glass seals with lead glass, said alloy being comprised of Cr 56%, Ni 42-43%, Be from small but effective amounts up to about 1%, Al from small but effective amounts up to about .25%, the balance of the alloy being substantially all Fe.

3. As an article of manufacture, an alloy suitable for use in the forming of metal to glass seals with lead glass, said alloy being comprised of Cr 56%, Ni 42%, Al .10-25%, Be .25-.'75%, balance Fe.

4. In a metal to glass seal, a metal part comprised of Cr 56%, Ni 42%, Al .10-25%, Be .30-.75%, balance Fe.

5. The method of forming a substantially gasfree alloy, comprised of Cr 56%, Ni 42-43%,

balance substantially all Fe which comprises forming a molten bath comprised of the said constituents in the said percentages, adding Al thereto in an amount at least sufficient to provide an alloyed percentage of Al up to about 25% in the solidified metal and then adding Be thereto in an amount at least sufiicient to provide an alloyed percentage of Be up to about 1% in the solidified metal, treating the molten alloy, with a flux to remove therefrom the Al and Be compounds formed during the said additions, and then casting and solidifying the alloy.

v 6. In a metal to glass seaL'a metal part comprised of an alloy comprised of Cr 56%, Ni

42-43%, Al in fractional percentages up to about 25%, Be in fractional percentages up to about 1%, balance Fe except for residual percentages of metal and metalloid impurities, each not in excess of about 20%.

7. A metal part for metal to glass seal, said part being comprised of an alloy comprised of Cr 54.25%, Ni 42%; Al 20%, Be 30%, balance substantially all iron except for incidental metal and metalloid impurities each in amounts not in excess of 20%.

VICTOR. O. ALLEN. CHARLES P. MARSDEN, JR. 

